Metal composition



Patented July 16, 1929.

UNITED STATES PATENT OFFICE.

GORTON R. FONDA, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A. CORPORATION OF NEW YORK.

METAL COMPOSITION.

No Drawing.

The present invention relates to a novel refractory metal composition or alloy consisting largely of tungsten and containing thorium and boron as elementary constituents, which is of particular utility as a lighting body in incandescent lamps. Filaments embodying my invention have a materially lower vapor pressure than ordinary tungsten filaments and hence may be operated at a given temperature with a longer life than ordinarv tungsten filaments, or may be operated with a higher lighting efliciency than tungsten with the same average length of life.

Although the production of my new incandescent material is not limited to any particular process, I find it convenient to employ in general the method of Coolidge U. S. Patent No. 1,082,933, of December 30, 1913.

Boron and thorium may be added to tungsten in an elementary state, or as reducible or decomposable compounds. The following examples of tungsten compositions containing thorium and boron material will illustrate my invention.

To the finely divided metallic tungsten may be incorporated by Weight 0.5% metallic thorium and 0.3% boron nitride. This mixture is sintered and swaged as described in the above Coolidge patent whereby the material is rendered ductile. It is then drawn into filaments as described in this patent. Thorium oxide may be used in place of a metallic thorium and boron sub-oxide or metalloidal boron may be used in place of boron nitride.

Boron in any of these forms appears to act as a reducing agent liberating metallic thorium. For example, to finely divided tungsten 0.7% thorium oxide, Th0,, and 0.5% to 0.3% boron nitride, BN, may be admixed, and the composition treated as above described to form ductile metal. In general I prefer to add less than one per cent by weight of thorium and boron respectively the boron preferably being of a lower proportion than the thorium and usually not in excess of one-half per cent. The intermediate product of sintered tungsten produced by the Coolidge process contains the admixed elements, that is in the above case, thorium oxide and boron Application filed May 1, 1923. Serial No. 635,971.

nitride. When this material is treated at a high temperature in hydrogen, the boron nitride dissociates into boron and nitrogen, and some'of the boron reduces the thoria to metallic thorium.

The product when subjected to swaging and drawing has normally the small grain structure characteristic of thoriated tungsten wire as described in Coolidge Patent No. 1,082,933. The specific electrical resistance of the swaged metal is materially higher than the specific resistance of substantially pure metallic tungsten, thoriated or non-thoriated-say, in the neighborhbod of 10% higher. It is substantially as workable as tungsten.

Incandescent filaments made in accordance with my invention may be mounted in vacuum lamps or in lamps containing a filling of gas or vapor, as described in Langmuir Patent No. 1,180,159. When filaments embodying my invention are to be operated in gasfilled lamps potassium silicate preferably is added to the raw batch of filament mix, as described in Patent No. 1,410,499, granted to Alad'ar Pacz, March 21, 1922.

What I claim as new and desire to secure by Letters Patent of the United States, is:

y 1. A metal composition consisting mainly of tungsten and containing less than one per cent respectively of thorium oxide and boron nitride.

2. A metal composition consisting largely of tungsten and containing a relatively small amount of thorium oxide and not more than one per cent of a boron material, the thorium oxide being in excess of the boron material.

3. A filament capable of operating at incandescence, said filament consisting largely of tungsten and containing thorium and boron, the thorium being in excess of the boron. I

4. A filament capable of operating at incandescence said filament consisting largely of tungsten but containing boron and a relatively small amount of thorium, the thorium being in excess of the boron.

In witness whereof, I have hereunto set my hand this 30th day of April, 1923.

GORTON R. FONDA. 

